General Mechanical

General Mechanical

APDL: prestressed harmonic analysis

    • antud
      Subscriber

      Hello everyone,


      I have a question regarding harmonic analysis of a prestressed structure as a part of master thesis work. To get acquainted with modal and harmonic analysis, I built a simple cantilever beam model and performed modal and harmonic analyses. These steps were successful.


      For my thesis, I am interested in orthoplanar bistable mechanisms; therefore, I was looking into the harmonic analysis of the same beam post-buckling, of pre-loaded with a displacement if you will. I have enclosed sketch of the beam with the keypoints used in the APDL code. My goal is to obtain a frequency response curve of the displacement amplitude to the frequency, as in the enclosed graph (this is the one obtained from the non-prestressed beam).


      Schematic of the beam


      Desired harmonic analysis result. This is the frequency response curve of the non-prestressed cantilever beam (keypoint 1 is clamped, keypoint 2 is free)


      Following some guides online, I have performed a static analysis with prestress effects and obtained the deformed/buckled beam. Firstly, I have conducted a modal analysis of the prestressed beam following this guide: http://mechanika2.fs.cvut.cz/old/pme/examples/ansys55/html/guide_55/g-ele/GELE3.htm in chapter 3.9. Subsequently, following chapter 4 of this guide, I have tried to conduct a harmonic analysis of the same prestressed beam, without much success unfortunately.


      The guide says to re-enter the solution after doing a static analysis and following it up with a reduced harmonic analysis. However, when I postprocess the results of the harmonic analysis (I create a plot of the displacement to the frequency), an empty plot is returned. So, my question is: how do I follow up my static analysis, in which I buckle my structure, with a harmonic analysis?


      I have tried antype,,restart from the static loadstep and last substep; however, the modes I find have an eigenfrequency of 1 Hz, which does not comply with the found modes in the modal analysis. For clarity, the used APDL code is also enclosed.


      Thank you in advance, and I hope you all stay safe during these times.

    • Erik Kostson
      Ansys Employee

      See in our help manual for linear perturbation analysis - so either do a static to modal to harmonic or static to full harmonic.


       


      The relevant chapter is:


      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v190/ans_str/strlinperturb.html


       


       

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